A semiconductor wafer or a liquid crystal display panel is a super precision part, so becomes defective due to extremely fine dust etc. For this reason, a production line of a wafer or liquid crystal display panel or the inside of apparatuses of the production line are spaces of high cleanliness. In this regard, the drive parts of semiconductor production apparatuses, liquid crystal display panel production apparatuses, etc. make use of large numbers of ball screws, linear guides, and other linear devices.
Such a ball screw, linear guide, or other linear device is provided with a raceway member which has a rolling element rolling part on its outer circumferential surface, a moving member which has a load rolling element rolling part which faces the rolling element rolling part on its inner circumferential surface and which can move relative to the raceway member, a plurality of rolling elements which are loaded rollably inside of a rolling element raceway which is formed by the rolling element rolling part and the load rolling element rolling part, and a rolling element recirculation path which connects a starting point and end point of the rolling element raceway to form an endless rolling element passage.
Explaining this using a ball screw as an example, the raceway member is constituted by a threaded shaft, the moving member is constituted by a nut, and the rolling elements are constituted by balls. A ball screw is provided with a threaded shaft which has a spiral ball rolling groove (rolling element rolling part) at its outer circumferential surface, a nut which has a load ball rolling groove (load rolling element rolling part) which faces the ball rolling groove (rolling element rolling part) of the threaded shaft, and a plurality of balls which are loaded rotably inside a spiral ball raceway (rolling element raceway) which is formed by the ball rolling groove (rolling element rolling part) and the load ball rolling groove (load rolling element rolling part). Further, if making the nut which is screwed to the threaded shaft and the threaded shaft rotate and move relative to each other through the balls, the threaded shaft and nut move relative to each other in the axial direction through the rolling action of the balls. Further, the ball screw is provided with a ball recirculation path (rolling element recirculation path) which connects a starting point and end point of the ball raceway to form an endless ball passage (rolling element passage).
In this regard, in this ball screw, when the nut and the threaded shaft rotate relative to each other, the balls roll while sliding upon receiving the composite force in the rotating direction and the axial direction, so at the contact parts of the balls and ball raceway, rolling friction and sliding friction simultaneously occur. Further, if the balls contact each other, the directions of rotation of the adjoining balls become opposite to each other, so the relative slip speed between the balls doubles and large frictional force is caused. For this reason, the practice has been to coat grease, oil, or another lubricant between the ball raceway and the rolling elements so as to try to lighten the frictional force.
Here, the rolling motion of the rolling elements causes the oil ingredient in the grease which is coated between the ball raceway and the rolling elements to form fine particles which splatter. This splattered fine particles becomes a cause of defects in the wafer, liquid crystal display panel, or other finished product. For this reason, in the case of semiconductor production apparatuses, liquid crystal display panel production apparatuses, and other cases where cleanliness is required, clean grease, vacuum grease (fluid lubricant), solid lubricants, etc. are used. Due to this, the amount of fine particles (oil ingredient) which is produced from the lubricant and the contact parts of balls with other balls is suppressed.
However, in recent years, in the semiconductor field, higher throughput (higher productivity) by higher speed conveyance and further cleanliness have been increasingly demanded. Even if employing the current means of using clean grease, vacuum grease, solid lubricants, and the like to suppress the production of such fine particles, the amount of suppression has been becoming insufficient. That is, in recent years, in the semiconductor field, advances have been made in higher integration, so the conductor patterns have become increasingly finer. The deposition of fine particles on the semiconductor wafer or liquid crystal display panel in the previous steps (in the process of product ion of semiconductors, the steps from the cutting of the silicon to fabricate the wafer to the formation of the circuits in the wafer and inspection of the conductive patterns of the circuits) causes problems in the products and is being increasingly averred. Furthermore, in addition to the higher integration, measures to deal with the increase in the amount of fine particles accompanying the higher speed of wafer conveyance systems aimed at improvement of the throughput (productivity) have become essential.
Here, as a linear guide which is used in a vacuum environment in the past, for example, the one which is shown in FIG. 7 is known (see Patent Document 1).
The linear guide 101 which is shown in FIG. 7 is provided with a raceway member 102 which has rolling element rolling parts 102a, a moving member 103 which has rolling element recirculation paths which include load rolling element rolling parts (not shown) which face the rolling element rolling parts 102a and can move relative to the raceway member 102, a plurality of rolling elements (not shown) which are arranged in the rolling element recirculation paths, and clearance seals 104 and 105 which are provided at the moving member 103 and close the clearance between the raceway member 102 and the moving member 103 without contacting the raceway member 102. The clearance seals 104 are attached by mounting screws 106 to the end parts of the moving member 103 in the axial direction.
Further, each of the clearance seals 104 which are attached to the end parts of the moving member 103 in the axial direction is comprised of a plurality of alternately stacked thin first and second plates 107 and 108 and a holding plate 109 to which these first and second plates 107 and 108 are attached. The first and second plates 107 and 108 which form that clearance seal 104 move along the guide rail raceway member 102 while maintaining a slight clearance without contacting the raceway member 102. Explaining this clearance, as shown in FIG. 8, the clearance β between the second plate 108 and the raceway member 102 forms a uneven shape which is larger than the clearance α between the first plate 107 and the raceway member 102. By making the clearance between the clearance seal 104 and the raceway member 102 a uneven shape, when lubricating oil evaporates and the gas flows between the clearance seal 104 and the raceway member 102, a large resistance is caused compared with the case of forming the clearance by a flat shape and the lubricant inside of the linear guide device can be better kept from vaporizing and leaking to the outside of the linear guide.
Further, in the past, as a ball screw which can be used in a clean environment, for example, the one which is shown in FIG. 9, has been known (see Patent Document 2).
In the ball screw 201 which is shown in FIG. 9, inside a concave part 204 of a nut 203, in the order from the inside in the axial direction, a ring-shaped space 205, a non-contact seal 206, a ring-shaped space 205, and a non-contact seal 206 are arranged. These are fastened by bolts 207 to the end face 204a of the concave part 204. Due to this, a space 208 which is surrounded by the adjoining non-contact seal 206 and spacer 205 and the threaded shaft 202 and a space 209 which is surrounded by the inside non-contact seal 206 and spacer 205 and the end face 204a of the concave part 204 are formed. These spaces 208 and 209 become grease pooling spaces.
In this way, an outside seal which is arranged at the outer most side of the nut 203 in the axial direction is made a non-contact seal 206 and grease pooling spaces 208 and 209 are provided, so compared with the case of making the outside seal a contact seal and providing grease pooling spaces, the production of dust due to wear of the contact seal is reduced. Further, compared with the case of making the outside seal a non-contact seal and not providing grease pooling spaces, the production of dust due to splattering of grease is reduced and the lubricating performance also becomes excellent.